This invention generally relates to photo responsive materials and methods for their use. More specifically, the invention relates to a direct write imaging film which is capable of having an image formed directly thereupon by a beam of light, without the use of any photo mask or negative.
Photo lithographic and/or photo etch techniques are widely used in the fabrication of printed circuit boards, semiconductor devices, the preparation of printing plates, and a number of other such processes. Such photo techniques generally employ one or more masks, also referred to as phototools. The phototool is used as a master in the exposure of other photosensitive materials. In general, materials used for phototools should have very high resolution and should be capable of presenting a high contrast image at imaging wavelengths. That is to say, the phototool material should have an image area which is highly absorbing of imaging wavelengths, and a background area which is highly transparent at imaging wavelengths.
A number of different media have been employed for the fabrication of photo masks. One group of materials comprises direct write media. In such materials, a beam of light, generally a high intensity beam of light from a laser, is scanned across a film so as to directly form an image thereupon. Systems of this type are advantageous insofar as they can be easily interfaced with computerized data storage and processing systems. Furthermore, the imaging media of this type generally have relatively low sensitivity to ambient illumination, and may be handled under normal room light.
Several different types of direct write films are known in the prior art. One group of films comprises ablation imaging films. In these materials, a high intensity beam of light, typically from a laser, impacts a body of imaging material and causes physical removal of the material by volatilization. One such process is shown in U.S. Pat. No. 5,521,050. Another direct write imaging film in which a beam of light ablates or degrades an imaging dye is shown in U.S. Pat. No. 5,747,197. A somewhat similar approach is shown in U.S. Pat. No. 5,256,506. As disclosed therein, a layer of light absorbing, ablatable dye-containing material is disposed atop a layer of ablation enhancing material. Both layers are highly absorbing of the beam of imaging light, and the layer of ablation enhancing material increases the sensitivity of the imaging medium by driving the volatilized dye-containing layer away from the film. While ablation imaging films are in wide use, the volatilization of a relatively thick layer of imaging material produces a significant volume of effluents which may be toxic, and in any event must be cleaned from the imaging apparatus.
Another approach to providing a direct write medium involves the use of photodispersable materials. In imaging films of this type, a layer of meltable material, typically a layer of metal, is disposed upon a substrate in a continuous sheet. A beam of light is impinged onto the layer and causes it to melt. The melted layer draws up into droplets through surface tension thereby lowering the optical density of the imaged area. In order to provide sufficient optical density in the nondispersed areas, these films generally require relatively thick layers of metal; hence, fairly large energy fluxes are required to cause dispersion. Examples of such imaging materials are found in U.S. Pat. No. 4,000,334 and U.S. Pat. No. 4,211,838.
There is a need for a direct write imaging film which has high resolution and high contrast, and which does not generate significant amounts of volatile material in its use. In addition, the imaged film should have very good dimensional stability and should be resistant to scratching, cracking and fading under ambient handling conditions.
The present invention provides a direct write imaging film which meets all of the foregoing criteria. The direct write imaging film of the present invention does not require any wet chemical processing, and may be used under ambient light conditions, and it is readily adaptable for use in computer controlled imaging systems of the type wherein a laser or similar light source is controlled so as to directly write upon a film. The imaged film of the present invention has a very high DMax and a very low DMin in the UV portions of the spectrum, but is highly transparent in both the image and background areas, at visible wavelengths. This produces a xe2x80x9csee-through imagexe2x80x9d having high contrast at UV wavelengths. This combination of transparencies makes the material of the present invention very useful as a phototool or photo mask material, since the see-through feature allows for ready alignment of the phototool, while the strong UV absorption produces a high contrast image.
As will be explained in further detail hereinbelow, the imaged areas of the film are highly resistant to fading or photo bleaching. The imaging medium is highly resistant to scratching or chemical damage; therefore, overlamination is not necessary. The imaging species of the present invention is molecular, and not particulate; therefore, high resolution is achieved. The materials of the present invention do not require any chemical processing, special ventilation, or special handling.
There is disclosed herein a direct write imaging film which includes a substrate having a first layer of a first material disposed thereupon and a second layer of a second material disposed in a superposed relationship with the layer of first material. The first layer has a higher absorbance for a first wavelength of light than it does for a second wavelength of light, which second wavelength of light is shorter than the first. The second layer has a lower absorbance for the first wavelength of light than does the first layer, and a higher absorbance for the second wavelength of light than does the first layer. The material of the first layer is capable of being disrupted by the first wavelength of light, and when it is, the adherence of the overlying portions of the second layer to the remainder of the imaging film is decreased so that those portions of the second layer which overlie the disrupted regions in the first layer are readily removable from the remainder of the imaging film.
In particular embodiments, the layer of first material comprises a layer of metal. In yet other embodiments, the layer of second material includes an ultraviolet absorbing dye therein. In specific embodiments, the ultraviolet absorbing dye is a member of a particular group of azo dyes.
In some embodiments, a heat dispersing layer is interposed between the first layer and the second layer. In other embodiments, a body of adhesive material is disposed atop the second layer, and this body of adhesive material functions to lift away portions of the second layer which overlie disrupted portions of the first layer.
Also disclosed herein is a method of preparing a phototool which method involves the use of the direct write imaging film of the present invention.